The disclosure of Japanese Patent Application No. 2000-228101 filed on Jul. 28, 2000 is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a one-way clutch and, more particularly, to a supporting structure suited for mounting a one-way clutch to an automatic transmission.
2. Description of Related Art
A one-way clutch is constructed such that a number of lock members (sprags, rollers, and so on) supported by a retainer are disposed between an outer race and an inner race and that end bearings are disposed on opposed sides of the lock members so as to maintain concentricity between the races. A one-way clutch is used as a mechanical element for various purposes. In particular, in the case where a one-way clutch is employed in an automatic transmission as a means for engaging a rotational element of a planetary gear constituting a speed-change mechanism with a transmission case, a state of engagement with the transmission case can be canceled automatically through inversion of a torque applied to the rotational element, unlike the case with a wet multiple-disc frictional engagement element. Therefore, the one-way clutch is effective as an engagement means that is on the release side when performing a speed-change operation of engaging one of different rotational elements and releasing the other simultaneously.
Conventionally, as an example of structures wherein such a one-way clutch is installed in and supported by a transmission, there is an art disclosed in Japanese Patent Application Laid-Open No. HEI 10-231863. In this example, when an outer race and an inner race are fitted to and supported by a case and a rotational member respectively, a predetermined clearance is left in a fitting portion between the outer race and the case, and the inner race and the rotational member are closely fitted to each other with a narrow clearance. Thereby, radial movements (decentering caused by rotation and so on) resulting from whirling of the rotational member fitted to the inner race are finally absorbed by the clearance between the outer race and the case, as movements transmitted to the inner race, the end bearings and the outer race of the one-way clutch. Even if the inner race has moved radially due to whirling of the rotational member, normal operation of the one-way clutch is guaranteed.
However, according to the supporting structure of the above related art, the weight of the outer race as a non-rotational member is supported by the end bearings. Thus, especially if the case has been enlarged in diameter due to an increase in capacity of the transmission or the like and if the one-way clutch to be fitted to the case has been enlarged in diameter, the weight of the outer race is increased correspondingly. For this reason, surface pressures applied to the end bearings are increased. Furthermore, because the rotational member leading to a planetary gear is connected to the inner race with almost no play left therebetween, not only an inertia force of the inner race but also an inertia force resulting from radial whirling of other rotational members connected to the inner race is received by the end bearings. As a result, surface pressures applied to the end bearings are further increased.
In consideration of such circumstances, the invention mainly aims at providing a one-way clutch supporting structure capable of ensuring durability of the one-way clutch by reducing surface pressures applied to end bearings of the one-way clutch.
In order to solve the above problem, according to one aspect of the invention, there is provided a one-way clutch supporting structure wherein one of an outer race and an inner race of a one-way clutch having end bearings disposed between the outer race and the inner race is fitted to a stationary member, wherein the other race is fitted to a rotational member, and wherein a clearance of a fitting portion between the one of the races and the stationary member is narrower than a clearance of a fitting portion between the other race and the rotational member.
According to the above aspect of the invention, the clearance of the fitting portion of one of the outer race and the inner race that is connected to the stationary member is narrowed, and the permanently stationary one of the races is prevented from being displaced greatly by the stationary member so that great radial loads are prevented from being applied to the end bearings. Therefore, surface pressures applied to the end bearings can be reduced, and durability of the one-way clutch is improved. Further, because radial movements of the rotational member fitted to the other race are absorbed by the clearance of the fitting portion to be fitted to the other race, a radial inertia force that is applied to the rotational member is not applied to the other race. Therefore, surface pressures applied to the end bearings can be reduced, and durability of the one-way clutch is improved.
In the above structure, it is more advantageous that the one of the races be radially supported by the stationary member while abutting thereon. In this structure, one of the races is radially supported by the stationary member while abutting thereon, whereby the weight of the one of the races as well as a radial load applied thereto is supported by the stationary member. Therefore, surface pressures applied to the end bearings can further be reduced.
Further, in the above structure, it is more advantageous that the one of the races be the outer race and that the other race be the inner race. In this structure, the end bearings are located peripherally inwardly of the outer race and, thus, have only to support the inner race having a small mass. Therefore, surface pressures applied to the end bearings can further be reduced.
Further, in the above structure, it is also advantageous that the fitting portion of the one of the races to be fitted to the stationary member be fixed at opposed ends thereof by snap rings. In this structure, the fitting portion between the one of the races and the stationary member is fixed at axial both ends thereof by the snap rings, whereby the one of the races is prevented from being inclined. Therefore, surface pressures applied to the end bearings can further be reduced.
Further, in the above structure, it is also advantageous that the one of the races be spline-fitted to the stationary member and that a bottom portion of a spline of the one of the races abut on a top portion of a spline of the stationary member. In this structure, the abutment portion between the one of the races and the stationary member requires high precision for the sake of close fitting. On the side of the stationary member, the top portion is provided on the spline. Thus, nothing more than cutting the top portion, that is easy to process, is required. Therefore, the man-hours necessary for processing the case can be reduced.
Further, in the above structure, the inner race may have an oil passage for supplying the end bearings with lubricating oil.
In this structure, because sliding surfaces of the end bearings can be reliably supplied with lubricating oil, durability of the one-way clutch is improved.